----- Original Message -----
From: "Fernando Gonzalez Gentile" <fgnzalez@xxxxxxxxxxxxx>
Subject: [OM] Re: F-stops [Was:
>
> Should I understand that the front nodal point is somewhere in front of
the
> lens? How does one find it? If so, I assume it is a virtual point, since
> rays coming out of the front would be parallel. But if rays come out
> parallel, does it make practical sense measuring the focal width at a
> certain point in front of the lens?
>
My less than perfect understanding of the front nodal point is that it can
be in front of the front element or within the lens depending on the lens
design. It corresponds to the point where a simple lens could be placed to
act as if it were the complex lens. For instance if the point source of
light weren't exactly at the focal plane, the rays would either converge or
diverge coming out the front of the lens. However they would act as if they
were coming from a simple lens having the diameter of the f-stop positioned
at the front nodal point.
-jeff
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